The present invention relates generally to an extension of an effective operational lifetime to stationary rechargeable batteries, and more particularly to stationary rechargeable batteries usable in energy storage devices (e.g., community energy storage and the like).
The electric utility system is evolving. The conventional utility includes one-way power flow from electricity generators to residential and commercial loads (through a multitude of transformers, transmission lines, and distribution lines). There is an expectation that future generations of utility systems will provide smart grid elements that include two-way power flow with multi-stakeholder interactions. Energy storage is a key central component of these solutions, and is important in the future success of the future generations. Energy storage, in the form of rechargeable batteries, may be used in many different locations and for a range of applications. A common attribute for these energy storage devices is that they will be high capacity stationary batteries.
Community Energy Storage is a concept for distributed energy storage initiated by American Electric Power, a large generator of electricity. Implementation of the concept is intended to provide a utility, and its customers, several benefits, including load leveling, back-up power, support for plug-in electric car deployment as well as grid regulation and improved distribution line efficiencies. As more renewable energy sources such as wind and solar are integrated into the smart grid, managing and storing energy is essential due to the intermittent nature of these power sources.
A trade organization, the Electricity Storage Association, has identified three major functional categories for large-scale stationary applications. These categories include power quality, bridging power, and energy management. Power quality is the provision of stored energy for seconds or less, as needed, to assure continuity of quality power. Bridging power is the provision of stored energy seconds to minutes to assure continuity of service when switching from one source of energy generation to another. Energy management is the provision of energy storage media to decouple the timing of generation and consumption of electric energy. An application of energy management is “load leveling” wherein a storage device is charged when energy cost is relatively low with the stored energy used when needed. Some degree of grid-independence is achieved, dependent upon the storage capacity and utilization.
High quality energy storage solutions are advantageously used in each of these categories. While the operational parameters may vary for the different uses, these storage solutions will typically include one or more rechargeable battery elements (e.g., cells, modules, assemblies, and combinations thereof and the like). Differing storage technologies may be appropriate for different aspects of these technologies. Each technology includes inherent limitations and disadvantages that inform practical and economic application of the technology in specific applications. (The development of improved and new technologies can skew the applications, so any assessment simply reflects a snapshot in time of the technology and application(s). Table 1 below includes a brief description of capability of various technologies.
TABLE 1MainDis-EnergyStorageAdvantagesadvantagesPowerApplica-Technology(relative)(relative)ApplicationtionPumpedHigh Capacity, Special Site 41StorageLow CostRequirementCAESHigh Capacity, Special Site41Low CostRequirement,uses Gas FuelFlowHigh Capacity,Low Energy21Batteries:Independent DensityPSB, VRB,Power & ZnBrEnergy RatingsMetal-AirVery High Electric41Energy DensityCharging isdifficultNaSHigh Power &Production 11Energy Densities,Cost, safetyHigh EfficiencyconcernsLi-ionHigh Power &High 13Energy Densities, ProductionHigh EfficiencyCost, requiresspecial charg-ing circuitNi—CdHigh Power &Not feasible 12Energy Densities,orEfficiencyeconomicalOtherHigh Power &High Produc-13AdvancedEnergy densities,tion CostsBatteriesHigh EfficiencyLead-AcidLow Capital CostLimited 13Cycle Life when deeplydischargedFlywheelsHigh PowerLow Energy13densitySMES,High PowerLow Energy14DSMESdensity, highproduction costE.C.Long cycle life, Low energy12Capacitorshigh efficiencydensity1—Fully capable/reasonable;2—Reasonable;3—Feasible;4—Not Feasible/Economical
The Li-ion technologies are a particular area of focus for development because this technology is a dual-use technology, being very useful for plug-in electric vehicles as well as stationary energy storage applications.
Lifetime and life cycle are two important parameters, among others, that are considered when selecting a particular storage technology for a particular application. Both parameters affect overall storage cost. A short lifetime increases the total cost of the storage device. Per year cost is one way to evaluate a cost of storing energy. Likewise, low cycle life also increases a total cost as the storage device will be replaced more often the lower the cycle life. Another Parameter that is applicable in certain applications is per-cycle cost. Per cycle cost is one way to evaluate a cost of storing energy in frequent charge/discharge applications, such as load leveling.
Costs and tradeoffs of the various technologies continue to change and evolve. What is needed is a flexible management system and method for efficiently operating energy storage devices to extend the lifetime, cycle life and consequently decrease the costs.